It is frequently desired to utilize barrier layers in semiconductor constructions. The barrier layers are provided to impede, and preferably prevent, migration of various materials therethrough. For instance, copper diffusion can be a problem when utilizing copper interconnects, and accordingly barrier materials are provided proximate the copper interconnects to preclude copper diffusion. A common copper-barrier material is tantalum nitride. However, it is difficult to deposit copper directly on tantalum nitride, and accordingly the tantalum nitride will typically be utilized as part of a tantalum nitride/tantalum bi-layer. The tantalum of the bi-layer is provided as a material onto which copper can be readily deposited. The tantalum is utilized in bi-layers with tantalum nitride, rather than alone, because pure tantalum is a poor barrier to copper diffusion. Pure tantalum can contain crystallization-induced columnar textures. Copper can permeate the tantalum along boundaries between adjacent columnar grains.
It is desired to form thinner copper lines as the level of integration increases, and copper barrier materials create numerous difficulties as copper line size decreases. For instance, it is typical to utilize a tantalum nitride/tantalum bi-layer having a thickness of from about 75 Å to about 150 Å, and there are numerous hardware/process control challenges to forming the bi-layer to be less than 50 Å. Thus, the copper diffusion barrier begins to limit the amount by which a copper line can be shrunk. Also, for barrier materials comprising tantalum there can be a challenge in that the columnar tantalum texture can create difficulties in forming the film to be 25 Å or less in thickness.
There have been some attempts to utilize barrier materials other than the tantalum nitride/tantalum bi-layer. For instance, tantalum nitride/ruthenium has been studied as a bi-layer material for utilization with copper. The tantalum nitride is an amorphous material which precludes copper diffusion, and the ruthenium is a seed material for growing the copper. The tantalum nitride/ruthenium bi-layer is utilized instead of a single barrier layer in that the ruthenium lacks suitable barrier properties and the tantalum nitride lacks suitable properties for growing copper thereon. Accordingly, the tantalum nitride is utilized as a barrier to copper diffusion and the ruthenium is utilized to provide a substrate onto which copper can be grown.
A continuing goal in semiconductor device fabrication is to decrease the dimension of circuit elements in order to increase the level of integration. Thus, it is desired to develop new barrier materials suitable for alleviating copper diffusion.
Barrier materials can have other applications besides the above-discussed applications of alleviating copper diffusion. For instance, barrier materials can be utilized to alleviate silicon diffusion, oxygen diffusion, and/or diffusion of numerous other materials.
In some applications, metal-insulator-metal (MIM) capacitors are formed over conductively-doped semiconductor pedestals (such as, for example, conductively-doped silicon pedestals). The electrode of the capacitor closest to the conductively-doped semiconductor pedestal (i.e., the lower electrode) can comprise a noble metal or near noble metal, such as, for example, gold, silver, platinum, palladium, etc. A diffusion barrier material can be provided between the lower capacitor electrode and the conductively-doped semiconductor pedestal in order to alleviate, and preferably prevent, oxygen diffusion from the high-k dielectric through the lower electrode and into the conductively-doped semiconductor. Various materials have been utilized for such barrier material, including, for example, tantalum nitride. However, there can be difficulties associated with the various prior art barrier materials, and it would therefore be desirable to develop new materials which can be utilized for barriers between a capacitor electrode and a conductively-doped semiconductor pedestal.
Persons of ordinary skill in the art will also recognize that there are numerous other applications for barrier materials, including, for example, between conductively-doped diffusion regions and conductive interconnects. It would be desirable to develop new barrier materials that are suitable for utilization in a wide variety of applications.